1. Field of the Invention
The present invention relates to dunnage bags for use in shipment of freight by truck, rail, aircraft, ship, and the like, and more particularly to an inflatable dunnage bag for such use having an increased bursting strength.
2. Description of the Prior Art
Inflatable, disposable dunnage bags are relatively inexpensive and provide a quick method of preventing lading and cargo damage that is caused by shifting and movement from unsecured loads. Inflatable dunnage bags are placed between individual and adjacent cargo pieces, or between cargo pieces and the freight carrier wall panels, in an initially deflated condition, and then are subsequently inflated with compressed air to a predetermined pressure, usually below a bag bladder bursting pressure. Most bags in use today are specially constructed such that they can withstand bursting pressure of 12-30 psig.
Such bags are typically comprised of a sealed plastic bladder such as polyethylene, which is surrounded by a multi-walled paper bag that functions to protect the bladder and increase the bursting strength thereof. A valve extends between the bladder and the outermost layer of the paper bags, such that the bladder and bag assembly can be simultaneously filled and expanded with compressed air from a compressed air source.
Inflatable dunnage bags are typically manufactured by folding a length of multiple-layered kraft paper onto itself at its edges, in order to form a rather long and overlapping seam generally along the bag centerline, thereby forming a multi-walled paper tube that has open ends. The sealed plastic bladder is inserted into the tube and then the paper tube ends are folded-over onto themselves. They are then either glued or sewn closed to form the completed air bag. The tube ends can even be closed by a combination of gluing and sewing.
Thus, it can be appreciated that when making multi-layered bags, the bag construction is ultimately limited by the ability to sew the multiple layers together, as well as being able to effectively fold and glue the layers together without the glued folds unraveling. There is also the associated problem of being able to acceptably cut the multiple layers of paper in one operation. Furthermore, construction of multi-layered air bags is relatively labor intensive, and the greater the number of layers, the greater the labor costs. Thus, a premium is certainly paid in trying to attain an inflatable dunnage bag which has a higher capacity to resist loading and hence, bursting through the addition of extra paper layers.